1. Field of the Invention
Device and methods consistent with the present invention relate to a heat assisted magnetic recording (HAMR) head including a near field light emitter having improved structure and arrangement.
2. Description of the Related Art
There is active interest in increasing a recording density in a technical field of magnetic information recording. As the recording density increases, the bit size of a recording medium that records unit information is decreased. However, since a signal magnetic field from a recording medium decreases as the bit size decreases, it is required to reduce noise in order to achieve a proper signal-to-noise ratio (SNR) during reproduction. Since noise originates predominantly from a magnetization transition region of the recording medium, it is possible to achieve a proper SNR by reducing the size of grains constituting a recording bit and thus reducing transition noise.
The spins of respective grains should maintain their recorded directions without thermal disturbance in order to stably maintain information recorded on the recording medium. For that purpose, the ratio of magnetic anisotropy energy to thermal energy, i.e., KuV/KBT should have a sufficiently large value of more than 60. Here, Ku is magnetic anisotropy energy density of a recording medium, V is the size of a grain, KB is the Boltzmann constant, and T is absolute temperature. Also, to achieve thermal stability in a high density recording medium having small grains, it is required to increase magnetic anisotropy energy density of the recording medium at a certain temperature. Since the magnetic anisotropy energy density is proportional to coercive force, a material having large coercive force needs to be used.
However, when a material having the large coercive force is used in order to achieve thermal stability, recording itself may be impossible due to a limitation in the intensity of a magnetic field generated from a magnetic recording head.
To address this problem, HAMR has been developed. In HAMR, heat is applied to the local area of a recording medium to reduce a coercive force of the local area so that the local area is easily magnetized by a magnetic field applied from a magnetic recording head. It is possible to achieve thermal stability using HAMR even when the grains of a recording medium are small.
A method of applying heat on the local area of the recording medium includes illuminating the recording medium using a laser ray.
FIG. 1 is a schematic perspective view of a related art HAMR head 1. Referring to FIG. 1, the HAMR head 1 includes a recording unit 1a which converts information into a magnetic signal and applies the converted magnetic signal onto a recording medium 2; a reproduction unit 1b including a reproduction device 9 which detects a recorded bit from the recording medium 2; and a light source 6 for thermal assistance. The recording unit 1a includes a recording pole 3 which applies a magnetic field onto the recording medium 2, a return pole 4 constituting a magnetic circuit in cooperation with the recording pole 3, and an induction coil 5 inducing the magnetic field on the recording pole 3. Assuming that the recording medium 2 moves in a direction A, a laser ray illuminated from the light source 6 such as a laser diode provides a light spot 7 on part of the recording medium 2, so that a coercive force of the part of the recording medium 2 illuminated by the light source 6 reduces right after the part of the recording medium 2 is heated by the laser ray. The part exposed to the light spot 7 is magnetized by leakage magnetic flux generated from the recording pole 3. Information recorded in this manner is reproduced using the reproduction device 9 such as a giant magnetoresistance (GMR) device, or the like.
To perform high density recording using the HAMR head 1, a light spot formed by a laser ray should be very small. For example, a light spot having a diameter of about 50 nm is required to realize a recording density of 1 Tb/in2. Accordingly, HAMR has been studied to obtain a small light spot using a near field light. However, it is difficult incorporate a near field light emitter including a light source into a magnetic head manufactured through a related art thin film process.